This is a proposal for secondary data analyses on the development of violence by young inner-city males in the context of their mental health problems and substance use. The proposal centers around four themes dealing with violence: (a) whether certain types of individuals tend to have distinctive developmental trajectories toward mental health problems, substance use, and violence in contrast to property crime. This knowledge is essential for the next step: (b) the impact of the co-occurrence of mental health problems and substance use on later violence, and (c) the impact of risk and protective factors on mental health problems, substance use, and violence. A final theme concerns: (d) whether service use and interventions alters individuals' trajectories toward violence. The data are from two samples of inner-city males in the Pittsburgh Youth Study (N = 1,009), who have been followed for 14 years between the ages of seven and 25. Assessments, using multiple informants, were undertaken first half-yearly, then yearly without gaps; eighteen assessments are available for the youngest sample and sixteen assessments are available for the oldest. Continuous measures of mental health and substance use were recorded at most assessment points, and diagnostic information is available for several assessments. A multitude of risk and protective factors have been measured over time. The prevalence of violence (such as robbery, assault, rape, and homicide) has been high. The study offers an unparalleled opportunity to advance basic and practical understanding of how mental health and substance use are developmentally related to violence in certain young males during the transition from childhood to early adulthood. The study results are likely to be relevant for prevention, intervention and service delivery systems pertaining to young males at risk for violence.